Reactor is a physics engine developed by the Irish software company Havok for use in Autodesk 3ds Max. Reactor was fully integrated with 3ds Max from versions 5 to 2011. In 3ds Max 2012, Reactor was replaced by a PhysX-based engine called MassFX.[1] Reactor was often used for realistic physics simulation that would be difficult or time-consuming to animate by hand.
Reactor is capable of computing rigid body, soft body, cloth, and rope collisions. Reactor can also simulate dynamics of any supported type interacting with a water volume, with adjustable viscosity and depth.
Reactor includes a large number of forces that can be used in simulation, apart from the default gravity: springs, dashpots, motors, wind, fractures (breakable objects), and a "toy car" type, with definable body/axis/wheels. Reactor also has many constraints available, including hinges, point-to-point constraints, prismatic constraints, car-wheel constraints, point-to-path constraints, and ragdoll constraints to simulate a lifeless body. In addition, Reactor is compatible with Space Warp modifiers in 3ds Max.